Digital watermarks are currently commonly used to authenticate content that has the watermark. The digital watermark is typically embedded into the content by means of digital signal processing. In the case of multimedia content, the watermark is usually imperceptible to the human eye/ear when the content is reproduced. In this manner, the authenticity of the content can be determined without the watermark producing undesirable side-effects.
The digital watermark is designed to be robust to digital manipulation so that if the content is changed slightly, the watermark is persistent. In other words, unless the quality of the content is significantly degraded or changed, the watermark is still recoverable. The watermark allows the ownership to be determined up to a degree where the modified content is likely to be no longer useful. In this manner, digital reproduction of the content is discouraged. Examples of digital watermark techniques in the context of content authentication are described in U.S. Pat. No. 5,915,027 to Cox et al. and U.S. Pat. No. 6,101,602 to Fridrich.
While digital watermarking has been used in the context of authentication, as detailed below, other applications have arisen with the increase of networking. For example, the explosion of the Internet in the past decade has caused a corresponding explosion in the delivery of multimedia content over the Internet. Audio and video clips are now being routinely distributed over the Internet. Live broadcasts of events are now starting to become commonplace. One concern is the maintenance of content quality as the multimedia content is distributed over the Internet. For various reasons, it has been found that as content is packetized and routed over the Internet, degradation occurs. The present invention relates to the monitoring of this degradation.